An x-ray imaging apparatus refers to an instrument that diagnoses a health condition by passing x-rays generated in an x-ray tube through a body of a human patient or an animal. The x-ray tube is provided with cathode and anode terminals and designed to generate the x-rays by allowing thermal electrons emitted from the cathode terminal to strongly impinge on the anode terminal. A high voltage needs to be developed between the anode terminal and the cathode terminal in order to ensure that the thermal electrons emitted from the cathode terminal strongly impinge on the anode terminal.
Shown in FIG. 1 is a functional block diagram of a portable x-ray imaging apparatus 1. Referring to FIG. 1, an AC-DC converting part 2 receives a commercial alternating current and then converts the same to a direct current. A DC-AC converting part 3 serves to convert the direct current to a high-frequency alternating current. A high-voltage transformer 4 transduces the high-frequency alternating current to a high-voltage alternating current. An AC-DC converting part 5 reconverts the high-voltage alternating current to a direct current which in turn is supplied to an x-ray tube 6 for generating x-rays.
A sensor part 7 senses the magnitude of a voltage applied to the x-ray tube 6 and supplies a signal indicative of the sensed voltage magnitude to a voltage control part 8. Furthermore, the sensor part 7 senses the magnitude of a current flowing through the x-ray tube 6 and supplies a signal indicative of the sensed current magnitude to a current control part 9. Based on the sensed voltage magnitude, the voltage control part 8 controls the magnitude of the voltage applied to the x-ray tube 6. The voltage control part 8 generates a pulse signal to control a switching-on and switching-off cycle of the DC-AC converting part 3, thereby controlling the magnitude of the voltage applied to the x-ray tube 6. Based on the sensed current magnitude, the current control part 9 controls the magnitude of the current applied to a filament transformer 10 to eventually control the magnitude of the current flowing through the x-ray tube 6.
With the conventional portable x-ray imaging apparatus 1, a large quantity of heat is generated during an operation process of the high-voltage transformer 4, the AC-DC converting part 5, the x-ray tube 6 and the filament transformer 10. In an effort to easily and rapidly dissipate the heat thus generated, the respective elements 4, 5, 6 and 10 of the portable x-ray imaging apparatus 1 are hermetically sealed within a housing part 12 filled with oil.
Due to the fact that the portable x-ray imaging apparatus 1 described above uses a commercial alternating current as a drive power source, it has a limit in that it can be used only in a place where an electric outlet is provided.
FIG. 2 is a functional block diagram of a conventional battery-powered x-ray imaging apparatus 1′ in which a battery is used as a drive power source. This battery-powered x-ray imaging apparatus 1′ uses a battery as its drive power source to overcome the limit of the portable x-ray imaging apparatus 1 noted above.
The battery-powered x-ray imaging apparatus 1′ includes a rechargeable battery 11, the electric power of which is supplied to an x-ray tube 6. In the battery-powered x-ray imaging apparatus 1′, a large number of dry cells are arranged in series to provide a high voltage corresponding to that of the commercial alternating current. This increases the weight and volume of the battery-powered x-ray imaging apparatus 1′, thereby reducing the portability thereof.
In recent years, a great deal of research efforts and capitals are invested in development of a battery-powered x-ray imaging apparatus which is light in weight and small in size. In particular, such an investment is concentrated on development of a small-sized and lightweight battery-powered x-ray imaging apparatus operable at a low voltage.
If a high-voltage battery is used in a battery-powered x-ray imaging apparatus that requires a constant level of electric power, the battery applies a relatively small current to a DC-AC converting part. In contrast, if use is made of a low-voltage battery, a large current flows through a current flow path extending from the battery to the DC-AC converting part. For this reason, a great loss of electric power occurs in the current flow path and a large quantity of heat is generated in the DC-AC converting part that performs a switching operation at a high speed.